The present invention relates on the one hand to a method for determining distance, and on the other hand to an arrangement for determining distance.
In refiners intended for paper pulp production, the size of the refining gap between a stator and a rotor is changed during operation as a consequence of wear on the mutually facing refining segments on the stator and the rotor. For reasons of quality, it is desirable to have good control over the size of the refining gap and to be able to compensate for wear, or to change the size of the refining gap for other reasons. Refiners of this type usually have long operating periods, often several months, or which reason it should be possible to effect monitoring of the size of the refining gap during operation.
In order to measure the size of the refining gap, it is customary to use sensors of magnetic type which are positioned in a stationary manner in the stator, with the end surface of the measuring head level with the surface of the refining segments. For sensor calibration, the rotor is first, while rotating and during idle running, moved axially in the direction towards the stator until the refining segments on the two come into contact with one another. In this state, the sensor is zeroed. By then reversing the rotor a predetermined distance, the sensor can be calibrated.
One of the disadvantages of such a procedure is that it can DC used only on machines in which the rotor can be operated very accurately, as otherwise the zeroing wear can be great, and calibration and checking of the sensor can furthermore be carried out only during idle running. Another disadvantage is that the positioning of the sensor in the surface of the refining segments results in continuous wear of the sensor during operation.
The object of the invention is to make easier and more reliable determination of the distance between the stator and the rotor possible in machines of the type indicated.
By using at least one sensor mounted movably in the stator, the sensor can be calibrated easily with regard to gain. Moreover, the possibility is afforded of checking the sensor by moving it a certain distance, with the rotor either at a standstill or rotating. For zero calibration, it is no longer necessary to move the rotor axially until contact is made between the refining segments, but it is sufficient to move the sensor into contact with the rotor.
The mobility of the sensor also makes it possible, in the event of contact between the refining segments on the rotor and the stator during operation, to reverse the sensor a little distance from its normal position level with the surface of the refining segment, so that further wear of the sensor is avoided. By using a number of sensors on the stator, it is also possible to measure and control any relative inclination between the stator and the rotor.
Further features and advantages of the solution according to the invention emerge from the description and the claims.
The invention will be described in greater detail below with references to exemplary embodiments shown in the drawings.